Method of treating mineral lubricating oils



Patented Oct. 9, 1934 UNITED STATES PATENT OFFICE METHOD OF TREATINGMINERAL LUBRICATING OILS No Drawing. Application May 6, 1932, SerialNo.609,776

-- 5 Claims. (01. 196-13) This invention relates to a'method of treatingmineral lubricating oils and it pertains more particularlyto the art ofpreparing lubricating oils stable to oxidation and sludging.

Petroleum is essentially'a mixture of hydrocarbons comprising severalgroups or homologous series of compounds, such as the paraflins,hydroaromatics, aromatics, polymethylenes, and various other series ofcompounds in which the hydrogen to carbon ratio is even lower than inthe above classes. A large number of individual compounds of each seriesare present and have different boiling points, physical and chemicalproperties. In the'various types of crude petroleum commonly known asparaffin base, naphthene or asphalt base, and mixed base oils, thesevarious series of hydrocarbons are present in different proportions. Forexample, in paraflln base oils such as those from the Appalachian field,there is a relatively high proportion of parafilnic hydrocarbons havinga chain structure and a high hydrogen to carbon ratio, whereas inthe-Gulf Coastal oils there is a high proportion of naphthenichydrocarbons and hydrocarbons with ring structures and low hydrogen tocarbon ratio.

. The mixed base oils, such as those from Oklahoma and the Mid-Continentarea, are in general intermediate between these two extreme types.

In normal refining of crude petroleum, the fractions of varyingdistillation ranges which are successively obtained by distillation ofthe .oils partake of the general character of the crude; for example,lubricating oils derived from Appalachian crudes will show parafiiniccharacteristics, whereas the lubricating oils derived from Gulf Coastaloils show naphthenic characteristics. The distillates from the mixedbase crudes, such as those from the Mid-Continent area, will showcharacteristics common to both the naphthenic and paraflinic oils. Animportant property of paraflinic lubricating oils is their low viscositytemperature coeflicient or rate of change of viscosity with temperature.Thisproperty makes them particularly suitable for certain lubricationproblems where high temperatures are encountered. At low temperaturesalso, these oils retain their fluidity better, an importantconsideration in cold weather operation of automobiles, (for example.For this reason it is very base oil. Paraffin base oils are arbitrarilyassigned a viscosity index of 100, naphthene base oils are assigned aviscosity index of 0, and mixed base oils lie between these extremes.@For example, if an oil shows a viscosity index ,of about 85 to 90, itis evident that the oil is predominately parafllnic in nature.

One of the common ways of increasing the parafllnic content of alubricating oil is to treat the oil with fuming sulfuric acid. The oiland acid are mixed and agitated in the proportion of about one to twopounds of fuming acid for each gallon of oil. The mixture is thenallowed to settle and the acid layer, comprising sulfuric acid and acidsludge es to the bottom and is drawn off. The top layer comprises an oilwhich is high in parafiinic compounds. Also, lubricating oil refined inthis way contains a relatively large quantity of sulfonic compoundswhich must be removed before the oil can be satisfactorily used for mostlubricating purposes, and this operation is often expensive and wastefulbecause of troublesome emulsions which are encountered. The quality ofthe acid treated lubricating oil can be fairly judged from two of itsproperties, that is, the viscosity index and stability against sludgeformation. The sludge stability is determined by bubbling air at therate of 10 litres per hour into a 250 cc. sample of oil at 340 F.Samples of 10 grams each are withdrawn at intervals and tested todetermine the amount of sludge formed for each 10 grams of oil. When theamount of sludge has increased to 10 mg. the number of hours ofoxidation is noted and the sludge stability of the oil is then expressedin hours for 10 mg. of sludge. The amount of sludge is determined bydiluting the 10 gram sample of oil with hexane and then filtering offthe hexane insoluble residue.

,The following table shows the sludge stability of a Mid-Continentlubricating oil distillate of 21.3 A. P. I. gravity, 101.9 Sayboltviscosity at 210 F., and a viscosity index of 54, when treated withdifferent quantities of fuming sulfuric acid.

From the above table it will be observed that a 2.7 pound acid treatincreased the viscosity index of the oil from 54 to 92, and the treatedoil hada sludge stability of 125 hours. Also, it will be noted that theyield is only 35%. From the above data it is apparent that a.largequantity of oil is temperature.

lost when highly stable oils are prepared by acid treating.

Mixed base oils can be made more paraflinic, as indicated by theviscosity index, by extracting the naphthenic and naphthenic-likecompounds, or sludge forming hydrocarbons, from the oil with organicsolvents. The solvent extraction may be performed with single solventsor with mixed solvents, and the extraction may be performed in one orseveral stages. Oils prepared by solvent extraction have very highviscosity indices, but the oils produced in this way are not stableagainst sludge formation. We have found that a light sulfuric acidtreatmentfollowing the step of solvent extraction will make the oilsvery resistant to oxidation. We have found that the oils prepared byorganic solvent extraction are particularly unstable as to sludgeformation, but a light acid treatment is also capable of making theseoils very resistant to sludge formation.

We will describe our preferred process by extracting a Mid-Continentlubricating oil distillate with a. single organic solvent, di(2chlorethyl) ether, and then follow this extraction with a light sulfuricacid treatment. We will use the same oil as described in connection withTable I, that is, a Mid-Continent lubricating oil distillate of 21.3 A.P. I. gravity, 101.9 seconds Saybolt viscosity at 210 F., and aviscosity index of 54. It should be understood that our process isapplicable to any mixed base lubricating oil. The lubricating oil anddi(2 chlorethyl) ether are mixed in the ratio of 3 volumes of solventfor each volume of oil, and the mixture is then agitated and heated tothe miscibility temperature. Generally the solvent or solvents aremiscible with the oil within the range of -210 F. In this particularexample we used a miscibility temperature of 155 F.

After the oil and solvent have been heated to the miscibilitytemperature, the mixture is cooled to a temperature below themiscibility temperature where the solvent and extract separate from thehighly paraflinic oil. The temperature at which this separation iseffected is called the "extraction temperature." In this particularexample we used an extraction temperature of about 65 F. It should'beunderstood that the extraction temperature may vary with different oilsand solvents, but generally the extraction temperature is at least 401?. below the miscibility The uppermost layer of oil comprises thehighly parafllnic oil, and this layer is referred to as the rafllna Thesolvent and extract are withdrawn from the bottom of the agitator, andthen the raflinate isstripped withaninert gas. 7 Generally, thestripping is performed at a somewhat elevated temperature.

The rafllnate is then given a light sulfuric acid treatment. In thisexample, we used one-half pound of 93% sulfuric acid for each gallon ofraiiinate. The oil and acid were mixed and agitated at about F. for ashort time, the acid layer was allowed to settle and was'then drawn off.The acid treating may be performed at any suitable temperature, butgenerally a temperature within the range of 20 to 200 F. issatisfactory. Also, the quantity of acid may be varied in accordancewith the quality of the oil desired, but generally from one-fourth toone pound of 80-98% sulfuric acid will give a very stable oil. It shouldbe understood that the more highly concentrated acid may be used insmaller quantities.

Typical results illustrating the cooperation between solvent extractionand acid treating are given in the following table.

Example 1 shows the viscosity index, sludge stability and yield of theoil after solvent extraction, and Example 2 shows the viscosity index,sludge stability and yield of the oil after solvent extraction followedwith alight acid treatment.

It will be observed from Example 1 in the above table that solventextraction, per se, produced an oil of high viscosity index. Beforeextracting, the oil had a viscosity index of 54, but by solventextraction this was raised to a viscosity index of 93. Notwithstandingthe high viscosity index,

the sludge stability of the oil is relatively low.

By comparing the oil prepared by solvent extraction, as set forth inExample 1 of Table II, with the oil prepared by acid treatment, as setforth in Example 1 of Table I, it will be observed that both oils havethe same sludge stability, but the oil prepared by solvent extractionhas a much higher viscosity index, that is, the solvent extracted oil ismore paraflinic than the acid treated oil. It will be observed fromExample 2 of Table II, that a one-half pound 93% acid treat applied tothe oil in Example 1 of Table II raises the sludge stability from 66hours to hours for 10 mg. of sludge. Also, the yield of oil is 55%,whereas with acid treating per se, see Example 2, Table I, the yield is35% fora 125 hour oil. So, by using a light acid treatment after solventextraction we can obtain a 55% yield of 125 hour oil having a viscosityindex of 94, whereas by acid treating alone, as shown in Example 2 ofTable I, a 35% yield of 125 hour oil having a viscosity index of 92 wasobtained. Also, the combination of solvent extraction and 93% acidtreating gave an oil with properties that could not be obtained with 93%acid treating alone.

A lubricating oil distillate of 22.8 A. P. I. gravity and 101 sec.Saybolt viscosity at 210 F. was given three successive di(2 chlorethyl)ether extractions and the railinate was then given a light acidtreatment. The volume of chlorinated ether used for each extraction was66% of the volume of oil. The following table shows the results fromthis treatment.

It will be observed that the light acid treatment raised the sludgestability of the solvent extracted 011 from about 60 hours to 231 hours.Also, the yield of finished product was 55% whereas if fuming acidtreatment alone had been used to produce a 231 hour oil, the yieldwould'have been much below 35%.

It is difllcult to explain why such a small amount of acid treatmentfollowing solvent extraction of an oil should be so effective in raisingthe sludge stability of the oil, and at the same time give a high yieldof finished product. Possibly the solvents remove the naphtheniccompounds that usually protect the sludge-forming compounds,-

thereby making the sludge-forming compounds of the oil more vulnerableto the action of acids.

As pointed out above in connection with acid treated oils, a largequantity of soluble sulfonic compounds remained dissolved in the acidtreated oil, and it is necessary to remove these sulfonic compoundsbefore the oil can be used for most lubricating purposes. Severalprocesses have been used to remove the sulfonic compounds, the mostcommon of which is to treat the oil with a soap solution. By using ourprocess of solvent extraction followed with a light acid treatment, weovercome the difliculty of having sulfonic com pounds dissolved in therafiinate. The solvents v remove, among other substances, thosecompounds which react with sulfuric acid and form sulfonic acids;consequently, when the oil is given a light acid treatment, the solublesulfonic compounds are not formed to any appreciable extent and theirremoval constitutes no problem nor entails serious loss of oil.

As pointed out in the above process of chlorinated ether extraction, itis necessary to strip the raflinate of the solvent dissolved therein,but it is very difiicult to remove the last trace of solvent from theoil. If all of the halogenated compound is not removed, it willeventually decompose and produce chlorine compounds which are verycorrosive. Also, if the oilis extracted with other organic compoundsthey will dissolve in the raflinate and it is frequently very diflicultor even impossible to remove the last trace. Frequently, the color ofthe oil is impaired when the oil is subjected to severe stripping. Also,if every trace of solvent is not removed from the oil, the oilfrequently becomes discolored and deteriorated in other ways. This isparticularly true of solvents such as furfural. We have found that bygiving the oil a light acid treatment subsequent to the steps of solventextraction and light stripping, the last traces of solvent that remainin the oil can be very satisfactorily removed and we thereby preventcorrosive and color forming compounds from remaining in the finishedoil.

The railinate, or highly parafiinic oil, which is to be given a lightacid treatment, may be obtained by extracting oil with any suitableselective solvent or mixture of solvents which will remove theconstituents responsible for low viscosity index. Examples of some ofthe single solvents suitable for extracting oils are halogenated ethers,nitroaryl compounds, aryl amines, phenols, halogenated esters, andheterocyclic compounds. The following table gives examples of some ofthe above compounds which may be used for extraction.

Table IV Methyl 2-chlorethyl ether di(2-chlorethyl) ether Methylchloropropyl ether Methyl 2-3 dichloropropyl ether Ethyl 2-3dichloropropyl ether Ethyl chloropropyl ether Table IV-C'ontinued2-chlorethyl propyl ether Dichlorisopropyl ether Dichlorpropyl etherNitrobenzene Nitrotoluene Nitroxylene Aniline Phenol Cresols Cresylicacid Ethyl chloracetate Ethyl dichloracetate Ethyl chlorpropionate2-chlorethyl acetate Methyl chloracetate 2-chlorethyl propionateFurfural Dioxane Pyridine Nitronaphthalene alpha dichlorohydrlnschlorohydrins Mixed solvents are also very effective for extractingmixed base lubricating oils, particularly the low boiling ketones,esters or ethers may be mixed with any of the solvents selected from theabove Table IV. The following table gives examples of some of the mixedsolvents that may be used for solvent extraction.

Table v Acetone and nitrobenzene Acetone and di(2-chlorethyl) etherAcetone and furfural Acetone and dioxane Acetone and paraldehyde Acetoneand dichlorobenzene Acetone and ethylene dichloride Acetone and phenolAcetone and aniline Acetone and pyridine Acetone and cresol Diacetonealcohol and nitrobenzene Diacetone alcohol and di(2-chlorethyl) etherMethyl ethyl ketone and di(2-chlorethyl) ether Methyl ethyl ketone andpyridine. Methyl ethyl ketone and di(2-chlorethyl)ether Methyl ethylketone and phenol Methyl propyl ketone and nitrobenzene Methyl propylketone and di(2-chlorethyl) ether Methyl isopropyl ketone and furfuralEthyl acetate and nitrobenzene Ethyl acetate and di(2-chlorethyl) etherEthyl acetate and furfural Ethyl acetate and nitrotoluene Ethyl acetateand paraldehyde Ethyl acetate and phenol Glycerine and phenol Glycerineand furfural Glycerine and aniline Glycol and aniline Glycol and phenolGlycol and furfural Propyl ether and nitrobenzene Isopropylether andnitrobenzene Isopropylether and chlorinated ethers Ethyl acetate anddioxane Ethyl acetate and ethylenedichloride Methyl acetate andnitrobenzene Methylacetate and di(2-chlorethyl) ether Methyl acetate andphenol Propyl acetate and nitrobenzene Propyl acetate anddi(2-chlorethyl) ether Table V-Continued Propyl acetate and phenolPropyl acetate and furfural Propyl acetate and dichlorobenzene .Butylacetate and phenol Butyl acetate and furfural Butyl acetate andparaldehyde Butyl acetate anddim-chlorethyl) ether Butyl acetate andnitrobenzene Ethyl propionate and nitrobenzene Ethyl propionate anddi(2-chlorethyl) ether Ethyl propionate and phenol Methyl propionate andnitrobenzene When any of the solvents set forth in Table IV or V areused to extract mixed base mineral oils, the ratio of solvent to oil ispreferably from one to 5 volumes of solvent for each volume of oil. Themixed solvents usually comprise from one to four volumes of ketone,alcohol, ester or ether 'for each volume of the other solvent. Forexample, one volume of acetone and about two volumes of nitrobenzene aremixed and used to extract one volume of oil. The process, temperaturesused,

etc., as set forth in connection with the process I of usingdi(2-chlorethyl) ether as a solvent, may in general be successfully usedwith'the solventsgiven in Tables IV and V.

When a mixed base lubricating oil distillate is extracted with any ofthe above solvents, the

cating oil distillate of 21.6 A. P. I. gravity, 114 seconds Sayboltviscosity and a. viscosity index of 56.5 was extracted with differentmixed solvents, and the following table shows the effect of suchextraction upon the viscosity index yield and sludge stability of theoil. One volume of oil was extracted with the mixed solvents set forthin the examples of the following table.

Table VI i Rati 1 Percent Viscosity Exam- Components com compo yield W mindex nents 1 Acetone and nitrobenune 1.5 0.521 87.5 2 do 66 3 1:2 98.03 Acetone and di(2- chlorethyl) ether.. 75. 6 2 1:1 87. 5icettgneanggiagflxanad 70 2 1:1 82.5

ce ne'an ehyde 00.8 a 3:1 84 6 Acetone and dibe 76 2 1.8:0.2 8i 7Acetone and ethylene dichloride.-- 64. 6 3 2:1 84. 5 8 Acetone andphenol- 79.6 1, 5i 0. 5:1 82 9 Ethyl acetate and nilrobenzene 70 1.50.6:1 88 10 Diacetone alcohol and nitrobenaena- 06 l. 5 0. 5:1 83. 6

viscosity index from 56.5 to a viscosity index of 81 or above.Notwithstanding the high viscosi index, or paramnieity of these oils,they are susceptible to sludge formation when used under oxidizingconditions. Most of the oils prepared .by the above extraction willproduce 10 mg. of

sludge in about sixty hours. Also the yield of oil after the acidtreatment will be of the order of 5 to 10% below the yield given in theabove table with the solvents alone, but if acid treating- .from'theabove data that a light acidtreatrnent following an organic solventextraction gives a higher yield of finished product than could beobtained by acid treating alone. prepared by solvent extraction andcombined light acid treating have a good color, and clay treating may beeliminated.

The term naphthenic hydrocarbons is employed in the specification andclaims in a generic sense to include the compounds that have a lowviscosity index and rapid sludge forming characteristics, examples ofwhich are the aroe mati'c, aromatic-like, oleflnes, polymethylenes,nitrogen and sulfur compounds.

The method used for mixed solvent extraction followed with a light acidtreatment may be the same as set forth hereinabove with single solvents.Also the oil may be extracted with a single solvent, then extracted witha mixed solvent, and then given a light acid treatment to raise theoxidation stability if desired. Also, if desired, the oils may be givena light acid treatment before the step of solvent extraction.

The theory set forth herein to'explain the unexpected results obtainedby sulfuric acid treating combined with solvent extraction oflubricating oils is not to be considered as limitations upon the scopeof our invention, and though the present invention has been described inconnection with the details of specific examples, neither is it Iintended that such examples shall be regarded as limitations upon thescope of the herein described invention except as set forth in theclaims.

We claim:

1. The process for preparing a ;lubricating oil which is highlyresistant to sludge formation from a mineral oil containing naphthenicand parafflnic hydrocarbons, which comprises extracting the oil with asolvent containing a halogenated ether and thereby separating the highlynaphthenic compounds from the paraflinic compounds,

Also, the oils then treating the highly paraflinic fraction with a smallquantity of strong sulfuric acid.

2. The process for preparing a lubricating oil which is highly resistantto sludge formation from a. mineral oil containing naphthenic andparafflnic hydrocarbons, which comprises extracting the oil with asolvent containing a halogenated ether and a ketone and therebyseparating the naphthenic hydrocarbons from the paraflinic hydrocarbons,and then treating the paraflinic hydrocarbons with a small quantity ofstrong sulfuric acid.

. 3. The process for preparing a lubricating oil which is highlyresistant to sludge formation from a mineral oil containing naphthenicand parafflnic hydrocarbons, which comprises extracting theoil with amixture of acetone and di(2-chlorethyl) ether and thereby removing thenaphthenic hydrocarbons from the parafllnic hydrocarbons, and thentreating thehighly paraflinic hydrocarbons with a small quantity ofsulfuric 1 acid.

4. The process for preparing a lubricating oil which is highly resistantto sludge formation from 1 a mineral oil containing sludge-forming andparaflinic hydrocarbons, which comprises heating and agitating the oilwith an organic solvent containing acetone and nitrobenzene, cooling themixture until the oil separates into a highly parafiinic fraction ofhydrocarbons and a fraction of sludge-forming hydrocarbons, and thentreating the highly paramnic fraction of oil with 98% sulfuric acid inthe proportion of about one to one-half pounds of acid per gallon ofoil.

STERLING H. DIGGS. JAMES M. PAGE, JR.

